The DCT uses an active optics system (AOS) to support, collimate, and maintain the surface figures of the primary and secondary mirrors. The AOS will operate in one of two modes: open-loop based on operating conditions and calibration data or closed-loop when external wavefront feedback is available. AOS software controls and electronics will adjust the mirrors’ position and actuator force to correct for figure distortions and atmospheric dispersion. AOS components for the DCT are currently being assembled in the primary mirror cell at a hangar at Pulliam Airport in Flagstaff.
Primary Mirror Support
The 4.2m primary mirror (M1) is supported by 120 axial actuators, 36 lateral actuators, and three tangential definer rods. The figure at top right depicts the main AOS components for the M1.
The axial actuators preserve the mirror's shape by receiving and translating signal input from the AOS, and adjusting force on various points across the mirror's surface. The locations of the axial actuators on the backside of the mirror (depicted at right) were carefully calibrated using a powerful laser tracker and other metrology equipment to ensure optimal positioning. Optical engineers from University of Arizona - College of Optical Sciences designed and tested the configuration as part of their work associated with figuring and polishing the primary mirror.
The 36 lateral actuators on the M1 support produce a force suite on the outer diameter of the mirror with feedback from the tangent definer force transducers. This force suite varies with elevation angle, eliminating gravitational sag which would occur if the supports were purely passive as the telescope is tipped toward the horizon.
Secondary Mirror Support
The 1.4m secondary mirror (M2) is mounted in a specially-designed vacuum support structure that connects to the upper ring of the mount support truss. The M2 vacuum support system maintains zero force on the mirror thus preserving its figure. The M2 axial supports change in position to maintain collimation between the primary and secondary mirror.
Fabrication and assembly of M2 Support components is currently underway.
FIRST LIGHT INSTRUMENTS